Want to post geolocation on a external api using getx - flutter

Question

I have already got the geolocation with longitude and latitude using the geolocation plugin with getx but now I want to post the same longitude and latitude on API with already present in the backhand the model is yet to be created and even the provider is also yet to be done and I don't know how and the location API post should run in the background once with the application opens up.
API body:-
{
"longitude":"55.5852",
"latitude":"77.6532"
}
Controller code:-
class RootController extends GetxController {
var latitude = 'Getting Latitude..'.obs;
var longitude = 'Getting Longitude..'.obs;
var address = 'Getting Address..'.obs;
final currentIndex = 0.obs;
final notificationsCount = 0.obs;
final customPages = <CustomPage>[].obs;
NotificationRepository _notificationRepository;
CustomPageRepository _customPageRepository;
StreamSubscription<Position> streamSubscription;
RootController() {
_notificationRepository = new NotificationRepository();
_customPageRepository = new CustomPageRepository();
}
#override
void onInit() async {
await getCustomPages();
getNotificationsCount();
if (Get.arguments != null && Get.arguments is int) {
changePageInRoot(Get.arguments as int);
} else {
changePageInRoot(0);
}
super.onInit();
getLocation();
}
#override
void onReady(){
super.onReady();
}
#override
void onClose(){
streamSubscription.cancel();
}
getLocation() async{
bool serviceEnabled;
LocationPermission permission;
serviceEnabled = await Geolocator.isLocationServiceEnabled();
if(!serviceEnabled){
await Geolocator.openLocationSettings();
return Future.error('Location Services are disabled.');
}
permission = await Geolocator.checkPermission();
if(permission == LocationPermission.denied){
permission = await Geolocator.requestPermission();
if(permission == LocationPermission.denied){
return Future.error('Location permissions are denied');
}
}
if (permission == LocationPermission.deniedForever){
return Future.error('Location permissions are permanently denied');
}
streamSubscription = Geolocator.getPositionStream().listen((Position position) {
latitude.value = 'Latitude:${position.latitude}';
longitude.value = 'Longitude:${position.latitude}';
getAddressFromLatLang(position);
print(latitude.value);
print(longitude.value);
});
}
Future<void> getAddressFromLatLang(Position position)async{
List<Placemark> placemark = await
placemarkFromCoordinates(position.latitude,position.longitude);
Placemark place = placemark[0];
address.value = 'address:${place.locality},${place.country}';
}
List<Widget> pages = [
HomeView(),
// EServicesView2(),
ReviewsView(),
MessagesView(),
AccountView(),
];
Widget get currentPage => pages[currentIndex.value];
/**
* change page in route
* */
void changePageInRoot(int _index) {
currentIndex.value = _index;
}
void changePageOutRoot(int _index) {
currentIndex.value = _index;
Get.offNamedUntil(Routes.ROOT, (Route route) {
if (route.settings.name == Routes.ROOT) {
return true;
}
return false;
}, arguments: _index);
}
Future<void> changePage(int _index) async {
if (Get.currentRoute == Routes.ROOT) {
changePageInRoot(_index);
} else {
changePageOutRoot(_index);
}
await refreshPage(_index);
}
Future<void> refreshPage(int _index) async {
switch (_index) {
case 0:
{
await Get.find<HomeController>().refreshHome();
break;
}
case 2:
{
await Get.find<MessagesController>().refreshMessages();
break;
}
}
}
void getNotificationsCount() async {
notificationsCount.value = await _notificationRepository.getCount();
}
Future<void> getCustomPages() async {
customPages.assignAll(await _customPageRepository.all());
}
}
what else should I do?